 Solution

The pipe object interface supports command-query separation: consuming an input changes state, while querying the result observes the current output without feeding another input. A client can inspect the result repeatedly, including an initial result when the concrete pipe defines one. That is useful for accumulated statistics.

The channel object interface instead packages an input update and its associated output into one call. For request-and-result processing this is simpler: the caller cannot forget which update precedes a query. A pipe caller must respect the intended order of operations, and interleaving other callers between consume and result can change the observation. A single channel object method is not automatically thread-safe either; synchronization is a separate property.

Neither object interface is universally better. The choice depends on whether clients need independent observation of state or a combined transformation step. The adapters below can reconcile their protocols, provided the initial-result policy is made explicit.